How to cook sunny side up

NZ Lifestyle Block - - The Good Life - The fi­nal ver­sion. The test ver­sion. Cook­ing and get­ting hot. In­side the fi­nal ver­sion.

I’VE BEEN FOOL­ING around with so­lar cooker de­signs for a while now.

The ini­tial tri­als in­volved sheets of stain­less-steel tem­po­rar­ily bent around a cast-iron Dutch oven. It seemed to work, but other things got in the way of fur­ther de­vel­op­ment.

Un­til now. With a spare day in hand, I marked and cut out two pieces of stain­less-steel sheet to a pat­tern that looked some­thing like a gi­ant or­ange peel seg­ment. Then I bent up tabs all along one side of one piece, and riv­eted one edge to the other sheet. A cou­ple of tri­an­gu­lar end-pieces com­pleted the re­flec­tor.

A quick look through the trea­sure trove I have sit­ting un­der a line of trees later, I pulled out some Dex­ion shelf fram­ing – it looks like over­sized Mec­cano – and used it to knock up a frame. We were in busi­ness (see the pic­ture at right). Or so I thought.

That par­tic­u­lar day there was a 40-knot sou’west gale and wind chill be­came the dom­i­nant fac­tor. A quick search on Google sug­gested that wind chill could in­deed be a prob­lem for a so­lar cooker, which most folk get over by wrap­ping the food in plas­tic, cov­er­ing the unit with glass, or by strate­gic place­ment of wind­breaks. I didn’t fancy the first idea and the last one seemed in­ef­fi­cient, so I drifted off to sleep pon­der­ing glass.

The next morn­ing, the penny dropped. Sit­ting un­der the trees was the very item to solve the prob­lem, dis­carded from a pre­vi­ous pro­ject. I once tried to heat wa­ter for an out­door shower us­ing a black­painted tank in an in­su­lated box, with a Subaru tailgate as the en­clos­ing glass. As a wa­ter heater it was a non-starter, but the box and the tailgate might just be the per­fect house for a so­lar cooker.

A quick hose-down, a quick hackaround of the Dex­ion, and there it was. It wasn’t long be­fore I was able to sniff de­li­cious smells waft­ing from the small gap above the sat­is­fy­ingly-warm glass.

The fo­cus seems quite tol­er­ant, in that I can leave it for 20 min­utes with­out hav­ing to shift the box to face the sun again. It’s also easy to know when you have the re­flec­tor tilted cor­rectly as the Dutch oven is bathed in light.

If I wanted to re­ally push things along and boil a ket­tle in 10 min­utes, it would take more re­flec­tor area, but for what we need it does just fine. For op­ti­mal per­for­mance the food ves­sel should be black, while any re­flec­tor fo­cus­ing on it should be as near to a mir­ror as prac­ti­ca­ble. The box should be in­su­lated, and painted black on the in­side as there’s no point in re­flect­ing so­lar energy back out of the box. The top should be sealed (to re­tain the heat) so ac­cess should be from the side or the back.

Now I just need to in­vent a se­lec­tive cloud-drag­ger which moves them - as Spike Mil­li­gan would have said - ‘in the gen­eral di­rec­tion of away’. It’s a funny thing but when you live with so­lar energy, you tend to no­tice clouds more.

This is the kind of set-up that lends it­self to slow cook­ing of soups, hot­pots and stews dur­ing still, clear win­ter days, brought to us free by a tech­nol­ogy which won’t be break­ing down any­time soon.

That can’t be too bad. ■

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